United Color Gems

As summer stretches out toward its final dog days, and the thermometer keeps bobbing toward the high end, you are probably feeling the need to cool down. We have some nice ice to help. As usual with us, it’s the jewelry kind of ice.

Let’s look at five amazingly lovely pieces of jewelry we’ve recently featured on our AGS Facebook page to help us take our minds off of the temperature.

First up, these blue topaz and peridot earrings, and blue topaz pendant, from Goshwara are as calming and cool as the ocean itself.

Staying with the light blues, we love this custom engagement ring from Tacori:

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We often come across a gemstone that inspires us to learn more about its origins and history, as we search out jewelry designs that feature it. Today’s blog spotlights the alternative birthstone for a month other than this one, December. We’re referring to tanzanite.

Tanzanite is the exquisite blue variety of the mineral zoisite that is only found in one part of the world. Named for its limited geographic origin in Tanzania, tanzanite has quickly risen to popularity since its relatively recent discovery.

Zoisite had been around more than a century and a half before this rare blue variety was found in 1967. Trace amounts of vanadium, mixed with extreme heat, cause the blue color – which ranges from pale blue to intense ultramarine with violet undertones.

Due to pleochroism—an optical phenomenon in which a substance displays different colors when seen from different angles—tanzanite must be cut properly to highlight the more attractive blue and violet hues, and deemphasize the undesirable brown tones.

The majority of tanzanite on the market today is heat treated to minimize the brown colors found naturally and to enhance the blue shades that can rival sapphire.

Tanzanite is still only found on a few square miles of land in Tanzania, near majestic Mount Kilimanjaro. Its price and availability are directly tied to mines in this region.

Between its deep blue color and its limited supply, tanzanite is treasured by many—whether you happen to be born in December or not!

A 78ct tanzanite pendant by TAKAT.

“Ohrid” tanzanite and diamond earrings by Yael Designs.

Tanzanite carved ring by Goshwara.

White and rose gold pendant by Simon G. Jewelry featuring tanzanite.

Trillion-cut tanzanite and diamond earrings by AG Gems.

The “Coco Ring” by Erica Courtney features tanzanite accented with diamonds.

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There are several varieties of gemstones that display optical phenomena, which describes the many ways light interacts with the structural features or inclusions (internal characteristics) in the gemstone. Often these gemstones will be fashioned in a particular way that best displays these effects.

The science of optical phenomena can be fascinating, although the mystery and allure of these effects are what initially attract us! In this article, we’ll discuss six of the most familiar (and magical) displays of optical phenomena in gemstones.

Adularescence

Adularescence is the phenomena typically seen in moonstone, which is a member of the feldspar family. It produces a billowy soft blue to milky white light that appears to move across the gemstone. This occurs when light hits the alternating layers of albite and orthoclase, which are two differing forms of feldspar within the gem.

The layers of feldspar interfere with the light rays causing them to scatter and the eye to observe adularescence. The effect is best seen when the gemstone is cut en cabochon [en CAB-ah-shawn]—that is, with a polished, domed top and a flat or slightly rounded base.

Burmese moonstone ring by Michael Schofield & Co.

Moonstone and diamond ring by United Color Gems.

Asterism

Asterism, or stars, relates to the four- or six-rayed star pattern of light produced by the fibrous inclusions, elongated needles, or growth tubes in a gemstone. This singular, celestial-like phenomenon is best seen in a gemstone cut en cabochon.

Blue star sapphire by Suna Bros.

Pink star sapphire by Suna Bros.

Chatoyancy

Chatoyancy [sha-TOY-an-cee] is also known as “cat’s eye.” Fine needle-like or fibrous inclusions within the gemstone are what causes this effect. Again, stones fashioned as cabochons display this effect the best.

Tiger Eye and diamond ring by NEI Group.

Cat’s Eye indicolite tourmaline and rubellite ring by AG Gems.

Color Change

A small number of gemstones display the color change optical phenomena. Depending on the lighting environment, the color change appearance can vary due to the shifting wavelengths. The technical term for this is photochromism or photochroism; “color-change” is a lot easier to say!

The best-known color changing gemstone is alexandrite. When viewed in sunlight, it appears greenish. When placed under incandescent light, it appears reddish. Other varieties of color-changing gemstones include sapphire, garnet, spinel, diaspore, and tourmaline.

Labradorscence [lab-ra-dor-es-cence] is an optical characteristic often seen in labradorite. The effect is a spectacular play-of-color that is metallic or iridescent, displaying blue, green, red, orange, and yellow. This is an interference effect within the gemstone caused by internal structures that selectively reflect only certain colors.

Labradorite ring by Lika Behar Collection.

Labradorite pendant by Lika Behar Collection.

Play-of-Color

Play-of-color is created by a combination of diffraction and interference and is the result of the microstructure of opal: the chameleon of a thousand colors!

Opals are made up of many layers of small, stacked spheres of silica. These spheres diffract light, splitting it into a spectrum of colors. The layers of these spheres create interference allowing certain colors to dominate, depending on the angle the opal is viewed.

Black opal and diamond ring from Lightning Ridge Collection by John Ford.